Summary

The story begins at night in the office of C. Auguste Dupin. An unnamed, first person narrator and Dupin are sitting in Dupin's back library smoking pipes and saying nothing. Prefect G- of the Parisian police interrupts to consult with Dupin and the narrator.

The Prefect partially describes a problem that is confusing him by saying that it is both simple and difficult. Dupin responds that it may be so simple that it is difficult. The Prefect is nearly bowled over with laughter at the idea that something could be so plain that it is too difficult to figure out.

After recovering, the Prefect explains that a document was stolen from someone in the royal apartments and it is being used as blackmail. The person who purloined (which means "to steal") the document is known because the person whom it was stolen from...